We continue our studies of the replication and partition mechanisms that account for the stable inheritance of unit-copy bacterial plasmids for which P1 plasmid prophage serves as exemplar. In the period of this report we have (1) provided evidence for a role of DNA looping in the control of plasmid replication, (2) demonstrated a biphasic relationship between the concentration of a plasmid-determined initiator and plasmid copy number, (3) established an in vitro system for mini-P1 plasmid replication with which to deepen our understanding of replication requirements and control, (4) characterized a lytic replicon of P1 that may possibly serve as an auxiliary plasmid replicon, (5) demonstrated an aggressive interference with plasmid maintenance by an overproduced partitioning protein, (6) constructed indicator plasmids for the identification of host factors involved in plasmid partitioning and (7) completed a comprehensive review of the biology of bacteriophage P1.